Abstract:

A backlight controller generating a scaling factor for scaling the
intensity of a backlight illuminating a LCD (LCD) is provided. The
backlight controller includes a histogram generator and a scaling factor
selector. The histogram generator generates a histogram in response to an
input frame image of the LCD. The scaling factor selector includes a
luminance distortion estimator and a loop controller. The luminance
distortion estimator estimates a luminance distortion for each candidate
scaling factor with reference to the histogram. The loop controller
selects a scaling factor among the corresponding to a maximum acceptable
distortion among the estimated luminance distortions, so as to scale the
intensity of the backlight.

Claims:

1. A backlight controller scaling the intensity of a backlight
illuminating a liquid crystal display (LCD), comprising:a histogram
generator generating a histogram for an input frame signal of the LCD;
anda scaling factor selector, comprising:a luminance distortion estimator
estimating a luminance distortion for each candidate scaling factor based
on the histogram; anda loop controller selecting a scaling factor
corresponding to a maximum acceptable distortion among the estimated
luminance distortions, so as to scale the intensity of the backlight.

2. The backlight controller according to claim 1, wherein the candidate
scaling factor is within a global upper boundary and a global lower
boundary of the scaling factor.

3. The backlight controller according to claim 1, further comprising:a
delay unit used for receiving a previous scaling factor and inputting the
previous scaling factor to the loop controller, wherein the scaling
factor selector obtains the scaling factor according to the previous
scaling factor.

4. The backlight controller according to claim 3, wherein the candidate
scaling factor is within a local neighborhood range around the previous
scaling factor.

5. The backlight controller according to claim 1, the scaling factor
further used for compensating the gray levels of the pixel signals of the
input frame signal corresponding to the input frame signal.

6. A scaling factor full range search method for searching a scaling
factor scaling the intensity of a backlight iluminating a liquid crystal
display (LCD), comprising the following steps of:generating a histogram
for an input frame signal of the liquid crystal display;estimating
luminance distortions for candidate scaling factors between an global
upper boundary and a global lower boundary of the scaling factor based on
the histogram;selecting the scaling factor corresponding to a maximum
acceptable luminance distortion among the luminance distortions;
andscaling the intensity of the backlight according to the scaling
factor.

7. The full range search method according to claim 6, further
comprising:compensating the gray levels of the pixel signals of the input
frame singnal according to the scaling factor.

8. The full range search method according to claim 6, further
comprising:receiving the maximum acceptable liminance distortion.

9. A scaling factor local range search method for searching a scaling
factor scaling the intensity of a backlight iluminating a liquid crystal
display (LCD), comprises the following steps of:generating a histogram
for an input frame signal of the LCD;receiving a previous scaling
factor;estimating luminance distortions for candidate scaling factors
within a local neighborhood range of the previous scaling factor;
andselecting the scaling factor corresponding to a maximum acceptable
luminance distortion among the luminance distortions; andscaling the
intensity of the backlight according to the scaling factor.

10. The local range search method according to claim 9, further
comprising:delaying the scaling factor by a frame time and then using the
scaling factor as the previous scaling factor.

11. The local range search method according to claim 9, further
comprising:compensating the input frame singnal according to the scaling
factor.

12. The local range search method according to claim 9, further
comprising:receiving the maximum acceptable liminance distortion.

13. The local range search method according to claim 9, wherein the step
of selecting the scaling factor corresponding to the amximum acceptable
luminance distortion is achieved by binary search method.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]The invention relates in general to a backlight controller, and more
particularly to a backlight controller capable of scaling backlight
luminance with reference to a histogram of the grey level of a frame
signal inputted to a liquid crystal display (LCD).

[0003]2. Description of the Related Art

[0004]Liquid crystal display (LCD) has been widely used in electronic
display products such as TV, computer monitor, notebook computer, mobile
phone, or persona digital assistant (PDA). An LCD includes a backlight
module and an LCD panel. The backlight module provides the backlight with
fixed luminance to pass the LCD panel. In the LCD panel, the rotation
angle of the liquid crystal molecules displays a frame image by
controlling the penetration of the backlight.

[0005]In a conventional LCD, the intensity of the backlight is fixed. When
the LCD wants to display a dark or black frame image, the liquid crystal
molecules cover the backlight via the rotation angle of the liquid
crystal molecules, so as to display the dark or the black frame image.
However, the continual generation of backlight increases the power
consumption by the backlight module and reduces the lifespan of the long
operating backlight module. Moreover, as the liquid crystal molecules can
not completely cover the backlight, the conventional LCD has lower
contrast ratio when displaying a dark or the black frame image, resulting
in poor display quality.

SUMMARY OF THE INVENTION

[0006]The invention is directed to a backlight controller and a method
thereof capable of overcoming the disadvantages of a conventional liquid
crystal display (LCD) backlight module such as more power consumption,
and shorter lifespan, lower contrast ratio when displaying dark or black
frame image, and poor display quality, and making the backlight module
using the backlight controller of the invention have lower power
consumption, longer life-span, better LCD contrast ratio and better
quality of frame image.

[0007]According to a first aspect of the present invention, a backlight
controller generating a scaling factor for scaling the intensity of a
backlight illuminating a LCD (LCD) is provided. The backlight controller
includes a histogram generator and a scaling factor selector. The
histogram generator generates a histogram in response to an input frame
image of the LCD. The scaling factor selector includes a luminance
distortion estimator and a loop controller. The luminance distortion
estimator estimates a luminance distortion for each candidate scaling
factor with reference to the histogram. The loop controller selects a
scaling factor corresponding to a maximum acceptable distortion among the
estemated luminance distortions, so as to scale the intensity of the
backlight.

[0008]According to a second aspect of the present invention, a full range
search method for searching a scaling factor is provided. The full range
search method searching a scaling factor for scaling the intensity of a
backlight illuminating a LCD (LCD) includes the following steps. Firstly,
a histogram is generated in response to an input frame signal of the LCD.
Next, a luminance distortion is estimated with reference to the histogram
for each candidate scaling factor. The candidate scaling factor includes
an absolute upper limit, an absolute lower limit and all the numeric
ranging between the absolute upper limit and the absolute lower limit.
Afterwards, a scaling factor corresponding to a maximum acceptable
luminance distortion among the luminance distortions is selected to scale
the intensity of the backlight.

[0009]According to a third aspect of the present invention, a local range
search method for searching a scaling factor is provided. The local range
search method searching a scaling factor for scaling the intensity of a
backlight illuminating a LCD (LCD) includes the following steps. Firstly,
a histogram is generated in response to an input frame signal of the LCD.
Next, the previous scaling factor is received. Then, a luminance
distortion is estimated with reference to the histogram for each
candidate scaling factor. The candidate scaling factor includes all the
numeric range near the previous scaling factor. Afterwards, a scaling
factor corresponding to a maximum acceptable luminance distortion among
the luminance distortions is selected to scale the intensity of the
backlight.

[0010]The invention will become apparent from the following detailed
description of the preferred but non-limiting embodiments. The following
description is made with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a block diagram of a LCD using a backlight controller
according to a first embodiment of the invention;

[0012]FIG. 2 is a block diagram of a backlight controller according to a
first embodiment of the invention;

[0013]FIG. 3 is a histogram of each pixel grey level of a frame signal FS
(N) of FIG. 1;

[0014]FIG. 4 is a correspondence curve of pixel grey level between the
frame signals FS (N) and FSβ (N) of FIG. 1;

[0015]FIG. 5 is a correspondence curve between pixel grey level of the
frame signal FS (N) of FIG. 1 and corresponding luminance error;

[0017]FIG. 7 is a flowchart of full range search method for searching a
scaling factor β (N) according to a first embodiment of the
invention;

[0018]FIG. 8 is a block diagram of a backlight controller according to a
second embodiment of the invention;

[0019]FIG. 9 is a correspondence curve between distortion Dβ' and
candidate scaling factor β' of FIG. 8; and

[0020]FIG. 10 is a flowchart of local range search method for searching a
scaling factor β (N) according to a second embodiment of the
invention.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment

[0021]Referring to FIG. 1, a block diagram of a LCD using a backlight
controller according to a first embodiment of the invention is shown. The
liquid crystal display (LCD) 10 includes a compensator 11, a backlight
module 12, an LCD panel 13 and a backlight controller 20. The backlight
controller 20 generates a scaling factor β (N) in response to a
frame signal FS (N) of an N-th frame, and outputs the scaling factor
β (N) to the compensator 11 and the backlight module 12. The
backlight module 12 reduces the original backlight luminance in response
to the scaling factor β (N) to generate a scaled backlight Lβ
(N), N is a natural number.

[0022]A frame signal FS (N) is received by the compensator 11 for
compensating the frame signal FS (N) in response to the scaling factor
β (N) to output a frame signal FSβ (N) to an LCD panel 13. The
LCD panel 13 displays a frame in response to the frame signal FSβ
(N).

[0023]Referring to FIG. 2, a block diagram of a backlight controller
according to a first embodiment of the invention is shown. The backlight
controller 20 includes a histogram generator 21 and a scaling factor
selector 22. The histogram generator 21 receives the frame signal FS (N),
and calculates the pixel grey level thereof to generate a histogram S (N)
as indicated in FIG. 3, wherein the histogram of the pixel grey level of
the frame signal FS (N) ranging 0˜255 are included. In the present
embodiment of the invention, the pixel data includes 8 bits, and the
pixel grey level has a numeric region of 0˜255.

[0024]The scaling factor selector 22 includes a luminance distortion
estimator 221 and a loop controller 222. The luminance distortion
estimator 221 estimates a distortion Dβ' corresponding to a
candidate scaling factor β' with reference to the histogram S (N),
wherein the candidate scaling factor β' is a real number larger than
or equal to 0, and smaller than or equal to 1. The loop controller 222
selects a scaling factor β (N) in response to the distortion
Dβ' and an error signal Dm, and outputs the selected scaling factor
β (N) to the backlight module 12 and the compensator 11. The scaling
factor β (N) is corresponding to the error signal Dm that, for
example, is a maximum acceptable distortion of the distortion Dβ'.

[0025]The backlight module 12 of the present embodiment of the invention
controls the luminance of the scaled backlight Lβ (N) to be equal to
the product of the luminance of the original backlight and the scaling
factor β (N). For example, when the scaling factor β (N) is
equal to 0.5, the luminance of the scaled backlight Lβ (N) is
substantially equal to a half of the luminance of the original backlight.

[0026]The compensator 11 adjusts the frame signal FS (N) according to the
equation: FSβ (N)=FS (N)/β (N), wherein a correspondence curve
of pixel grey level between frame signals FS (N) and FSβ (N) is
shown in FIG. 4. In FIG. 4, the scaling factor β (N) is equal to
0.5, but each pixel grey level of the frame signal FSβ (N) is
substantially equal to a double of the pixel data FS (N). Thus, when the
luminance of the scaled backlight Lβ (N) of the backlight module 12
is reduced to a half of the original backlight, the frame signal FSβ
(N) is increased to be a double of the frame signal FS (N) so as to
correct the frame.

[0027]Thus, when a dark or black frame is to be displayed on the LCD 10,
the backlight controller 20 of the present embodiment of the invention
can effectively generate a corresponding scaling factor β (N) to
reduce the luminance of the scaled backlight Lβ (N) of the backlight
module 12. Thus, the LCD 10 of the present embodiment of the invention
effectively overcomes the disadvantages of a conventional LCD backlight
module, such as consuming more power, and having shorter lifespan, lower
contrast ratio when displaying dark or black image frame, and poor
display quality.

[0028]As indicated in FIG. 4, the pixel data whose grey levels of the
frame signal FS (N) are larger than 127 can only be corrected to be 255
in the frame signal F Sβ (N), not doubled. Thus, a luminance error
IE (K) will occur when displaying the pixels, wherein K is larger than or
equal to 128, and is smaller than or equal to 255. The correspondence
between pixel grey level of the frame signal FS (N) of FIG. 1 and
corresponding luminance error IE (K) is shown in FIG. 5.

[0029]The luminance distortion estimator 221 of the present embodiment of
the invention accumulates each grey level of the frame signal FS (N) and
its corresponding luminance error IE (K) with reference to the histogram
S (N) to obtain a distortion Dβ (N) corresponding to the scaling
factor β (N) and the frame signal FS (N), wherein a correspondence
curve between distortion Dβ' and candidate scaling factor β' is
shown in FIG. 6.

[0030]The loop controller 222 of the present embodiment of the invention
provides all candidate scaling factor β' ranging between 0˜1
to the luminance distortion estimator 221 by the full range search method
to search for the corresponding distortion Dβ'. Afterwards, the loop
controller 222 finds out the scaling factor β (N) and the distortion
Dβ (N) in response to the error signal Dm.

[0031]Thus, the backlight controller 10 of the present embodiment of the
invention can receive the error signal Dm, that is, the maximum
acceptable distortion of the distortion Dβ', via the loop controller
222, and accordingly selects a scaling factor β (N) among the
candidate scaling factors β' to reduce the luminance of the original
backlight. By doing so, the backlight controller 10 of the present
embodiment of the invention has the advantage of setting an upper limit
to the luminance error in the frame image with reference to the error
signal Dm to reduce the luminance error in the frame image of the LCD 10.

[0032]Referring to FIG. 7, a flowchart of full range search method for
searching a scaling factor β (N) according to a first embodiment of
the invention is shown. Firstly, the method begins at step 702, a
histogram S (N) is generated by the histogram generator 21 in response to
a frame signal FS (N). Next, the method proceeds to step 704, an error
signal Dm substantially equal to the maximum acceptable distortion of the
distortions Dβ' is received by the loop controller 222.

[0033]Then, the method proceeds to step 706, all of the distortions
Dβ' corresponding to the candidate scaling factors β' ranging
between 0˜1 are estimated with reference to the histogram S (N).
Afterwards, the method proceeds to step 708, a scaling factor β (N)
is selected among the candidate scaling factors β' by the loop
controller 222, wherein the scaling factor β (N) corresponds to the
maximum distortion of all of the distortions Dβ' smaller than or
equal to the error signal Dm. In the present invention, the scaling
factor β (N) corresponds to the distortions Dβ' equal to the
error signal Dm, which is substantially the maximum acceptable
distortion.

[0034]Then, the method proceeds to step 710, the scaling factor β (N)
is outputted to the backlight module 12 by the loop controller 222, and
the original backlight is reduced to the scaled backlight Lβ (N),
wherein the luminance of the scaled backlight Lβ (N) is
substantially equal to the product of the luminance of the original
backlight and the scaling factor β (N). Afterwards, the method
proceeds to step 712, scaling factor β (N) is outputted to the
compensator 11 by the loop controller 222. The compensator 11 compensates
the frame signal FS (N) and accordingly outputs a frame signal FSβ
(N) to the LCD panel 13 to display a frame image.

[0035]The backlight controller of the present embodiment of the invention
calculates all pixel grey levels of a frame signal, and obtains all of
the distortions corresponding to candidate scaling factors with reference
to the histogram. The backlight controller of the present embodiment of
the invention further receives a maximum acceptable distortion of the
distortions, and accordingly selects a better scaling factor referencing
the luminance distortions. Thus, the backlight controller of the present
embodiment of the invention effectively overcomes the disadvantages of a
conventional LCD backlight module, such as more power consumption, and
shorter lifespan, lower contrast ratio when displaying darker colors, and
poor display quality, and makes the backlight module using the backlight
controller of the invention have lower power consumption, longer
life-span, better LCD contrast ratio and better quality of frame image.

[0036]Moreover, the backlight controller of the present embodiment of the
invention can further set an upper limit with reference to an error
signal to the luminance error in the frame image of the LCD of the
present embodiment of the invention. By doing so, the LCD using the
backlight controller of the present embodiment of the invention is
further advantaged by a lower luminance error in the frame image.

Second Embodiment

[0037]Referring to FIG. 8, a block diagram of a backlight controller
according to a second embodiment of the invention is shown. The backlight
controller 80 of the present embodiment of the invention differs with the
backlight controller 20 of the first embodiment of the invention in that
the backlight controller 80 further includes a delay unit 83. The delay
unit 83 receives and delays the frame time of a scaling factor β
(N), and then outputs the delayed scaling factor β (N). The loop
controller 822 of the present embodiment of the invention differs with
the loop controller 222 of the first embodiment of the invention in that
the loop controller 822, by way of a local range search method for
example, uses all the numeric numbers within a numeric region R of the
previous scaling factor β (N-1) as candidate scaling factors
β', and find out a scaling factor β (N) among the candidate
scaling factors β'. The relation between the numeric region R and
previous scaling factor β (N-1) is shown in FIG. 9.

[0038]Referring to FIG. 10, a flowchart of local range search method for
searching a scaling factor β (N) according to a second embodiment of
the invention is shown. The local range search method of the present
embodiment of the invention scaling factor β (N) differs with the
full range search method of the first embodiment of the invention in that
before step 706, the local range search method further includes step 1005
and step 1006. In step 1005, previous scaling factor β (N-1) is
provided to the loop controller 822 by the delay unit 83. In step 1006,
the loop controller 822 uses all the numeric numbers within a numeric
region R near the previous scaling factor β (N-1) as the candidate
scaling factors β', and finds out a corresponding distortion
Dβ' from the candidate scaling factors β'. After step 708, the
local range search method further includes step 1009, a scaling factor
β (N) is received, delayed and outputted by the delay unit 83, and
the delayed scaling factor β (N) is used as a previous scaling
factor β (N-1) when finding the scaling factor β (N) next time.

[0039]In the present embodiment of the invention, the scaling factor
β (N) is searched by the loop controller 822 according to the local
range search method. However, the loop controller 822 can select a
scaling factor β (N) among the scandidate scaling factors β'
according to other methods. For example, the binary search method is used
to find out a scaling factor β (N) within the numeric region R.

[0040]In most cases, the luminance levels in two subsequent frame images
are substantially the same, so that the numeric numbers of scaling
factors β (N-1) and β (N) of two subsequent frame images are
also very close. Thus, the backlight controller 80 of the present
embodiment of the invention can effectively find out the scaling factor
β (N) within the numeric region R near the scaling factor β
(N-1) of previous frame image by local range search. Thus, apart from the
advantages that the backlight module has lower power consumption, longer
life-span, better LCD contrast ratio and better quality of frame image,
the backlight controller of the present embodiment of the invention is
further advantaged by saving the operation resources for the loop
controller in searching the scaling factor.

[0041]While the invention has been described by way of example and in
terms of a preferred embodiment, it is to be understood that the
invention is not limited thereto. On the contrary, it is intended to
cover various modifications and similar arrangements and procedures, and
the scope of the appended claims therefore should be accorded the
broadest interpretation so as to encompass all such modifications and
similar arrangements and procedures.